U.S. patent application number 13/906151 was filed with the patent office on 2014-12-04 for formed ceramic substrate composition for catalyst integration.
This patent application is currently assigned to CORNING INCORPORATED. The applicant listed for this patent is CORNING INCORPORATED. Invention is credited to Thorsten Rolf Boger, Gregory Albert Merkel, Zhen Song.
Application Number | 20140357474 13/906151 |
Document ID | / |
Family ID | 51023101 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140357474 |
Kind Code |
A1 |
Boger; Thorsten Rolf ; et
al. |
December 4, 2014 |
FORMED CERAMIC SUBSTRATE COMPOSITION FOR CATALYST INTEGRATION
Abstract
Disclosed herein are formed ceramic substrates comprising an
oxide ceramic material, wherein the formed ceramic substrate
comprises a low elemental alkali metal content, such as less than
about 1000 ppm. Also disclosed are composite bodies comprising at
least one catalyst and a formed ceramic substrate comprising an
oxide ceramic material, wherein the composite body has a low
elemental alkali metal content, such as less than about 1000 ppm,
and methods for preparing the same.
Inventors: |
Boger; Thorsten Rolf; (Bad
Camberg, DE) ; Merkel; Gregory Albert; (Corning,
NY) ; Song; Zhen; (Painted Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING INCORPORATED |
Corning |
NY |
US |
|
|
Assignee: |
CORNING INCORPORATED
Corning
NY
|
Family ID: |
51023101 |
Appl. No.: |
13/906151 |
Filed: |
May 30, 2013 |
Current U.S.
Class: |
502/67 ;
502/87 |
Current CPC
Class: |
B01J 29/763 20130101;
C04B 2235/9607 20130101; C04B 2235/3213 20130101; B01D 2255/50
20130101; B01J 21/14 20130101; C04B 2235/3227 20130101; C04B
2235/3262 20130101; C04B 2235/725 20130101; B01J 35/108 20130101;
C04B 2235/3232 20130101; C04B 35/478 20130101; C04B 35/195
20130101; C04B 2235/3201 20130101; B01J 35/04 20130101; C04B
2235/3239 20130101; B01D 53/9413 20130101; C04B 2111/0081 20130101;
B01J 37/0246 20130101; B01J 35/1042 20130101; B01D 2255/9207
20130101; B01D 2258/012 20130101; C04B 2235/3208 20130101; C04B
2235/3279 20130101; C04B 2235/3225 20130101; B01D 2255/9205
20130101; C04B 38/0006 20130101; B01D 2255/20761 20130101; C04B
2235/3275 20130101; C04B 35/195 20130101; C04B 38/0074 20130101;
B01J 35/1004 20130101; C04B 2235/3241 20130101; C04B 2235/42
20130101; B01J 23/04 20130101; C04B 2235/3272 20130101; B01J 37/10
20130101; C04B 2235/3215 20130101; B01D 53/944 20130101; C04B
38/0006 20130101; C04B 2235/3284 20130101; C04B 2235/727 20130101;
C04B 2235/3229 20130101; C04B 2235/3244 20130101 |
Class at
Publication: |
502/67 ;
502/87 |
International
Class: |
B01J 29/80 20060101
B01J029/80 |
Claims
1. A formed ceramic substrate comprising at least about 75% by
weight cordierite, wherein said formed ceramic substrate comprises
an elemental sodium content of less than about 1000 ppm, and has a
porosity of at least about 55%.
2. The formed ceramic substrate according to claim 1, wherein the
elemental sodium content is less than about 800 ppm.
3. The formed ceramic substrate according to claim 1, wherein the
elemental sodium content is less than about 650 ppm.
4. The formed ceramic substrate according to claim 1, wherein the
elemental sodium content is less than about 500 ppm.
5. The formed ceramic substrate according to claim 1, wherein the
porosity is at least about 62%.
6. The formed ceramic substrate according to claim 1, wherein the
porosity is at least about 64%.
7. The formed ceramic substrate according to claim 1, wherein the
porosity is at least about 66%.
8. A composite body comprising: a formed ceramic substrate
comprising at least about 75% by weight cordierite; and at least
one catalyst, wherein the formed ceramic substrate has an elemental
sodium content of less than about 1000 ppm.
9. The composite body according to claim 8, wherein the elemental
sodium content is less than about 800 ppm.
10. The composite body according to claim 8, wherein the elemental
sodium content is less than about 650 ppm.
11. The composite body according to claim 8, wherein the elemental
sodium content is less than about 500 ppm.
12. The composite body according to claim 8, wherein the at least
one catalyst is in a washcoat applied to the formed ceramic
substrate in an amount of at least about 5 grams per liter of
formed ceramic substrate.
13. The composite body according to claim 8, wherein the at least
one catalyst is chosen from zeolite catalysts.
14. The composite body according to claim 8, wherein the at least
one catalyst comprises a chabazite catalyst.
15. The composite body according to claim 8, wherein the at least
one catalyst comprises a metal-exchanged chabazite catalyst.
16. The composite body according to claim 15, wherein the
metal-exchanged chabazite catalyst is a copper-exchanged chabazite
catalyst.
17. The composite body according to claim 8, having a mean
coefficient of thermal expansion less than about
3.times.10.sup.-6.degree. C..sup.-1 from about 25.degree. C. to
about 800.degree. C.
18. A method for preparing a composite body having a substantially
maintained catalytic BET surface area of at least about 55% after
thermal aging at about 800.degree. C. for about 64 hours in air
containing about 10% by volume of H.sub.2O, said method comprising
the steps of: providing a formed ceramic body prepared from a
substrate composition comprising at least about 75% by weight
cordierite, wherein the batch components of the substrate
composition are chosen such that the content of elemental sodium
content in the formed ceramic body is less than about 1000 ppm; and
applying at least one catalyst to the formed-ceramic body.
19. The method according to claim 18, wherein the content of
elemental sodium in the composite body is less than about 800
ppm.
20. The method according to claim 18, wherein the content of
elemental sodium in the composite body is less than about 650
ppm.
21. The method according to claim 18, wherein the content of
elemental sodium in the composite body is less than about 500
ppm.
22. The method according to claim 18, wherein the at least one
catalyst is in a washcoat applied to the formed ceramic body in an
amount of at least 5 grams per liter of formed ceramic body.
23. The method according to claim 18, wherein the at least one
catalyst is chosen from zeolite catalysts.
24. The method according to claim 18, wherein the at least one
catalyst comprises a chabazite catalyst.
25. The method according to claim 18, wherein the at least one
catalyst comprises a copper-exchanged chabazite catalyst.
26. The method according to claim 18, having a substantially
maintained catalytic BET surface area of at least about 60% after
thermal aging at about 800.degree. C. for about 64 hours in air
containing about 10% by volume of H.sub.2O.
27. The method according to claim 18, having a substantially
maintained catalytic BET surface area of at least about 70% after
thermal aging at about 800.degree. C. for about 64 hours in air
containing about 10% by volume of H.sub.2O.
28. A method for preparing a composite body having substantially
maintained nitric oxide conversion efficiency at least about
200.degree. C. of at least about 80% after thermal aging at about
800.degree. C. for about 5 hours in air containing about 10% by
volume of H.sub.2O, said method comprising the steps of: providing
a formed ceramic body prepared from a substrate composition
comprising at least about 75% by weight cordierite, wherein the
batch components of the substrate composition are chosen such that
the content of elemental sodium content in the formed ceramic body
is less than about 1000 ppm; and applying at least one catalyst to
the formed ceramic body.
29. The method according to claim 28, wherein the content of
elemental sodium in the composite body is less than about 800
ppm.
30. The method according to claim 28, wherein the content of
elemental sodium in the composite body is less than about 650
ppm.
31. The method according to claim 28, wherein the content of
elemental sodium in the composite body is less than about 500
ppm.
32. The method according to claim 28, wherein the at least one
catalyst is in a washcoat applied to the formed ceramic body in an
amount of at least about 5 grams per liter of formed ceramic
body.
33. The method according to claim 28, wherein the at least one
catalyst is chosen from zeolite catalysts.
34. The method according to claim 28, wherein the at least one
catalyst comprises a chabazite catalyst.
35. The method according to claim 28, wherein the at least one
catalyst comprises a copper-exchanged chabazite catalyst.
36. The method according to claim 28, having a substantially
maintained nitric oxide conversion efficiency at least about
200.degree. C. of at least about 90% after thermal aging at about
800.degree. C. for about 5 hours in air containing about 10% by
volume of H.sub.2O.
37. The method according to claim 28, having a substantially
maintained nitric oxide conversion efficiency at least about
200.degree. C. of at least about 95% after thermal aging at about
800.degree. C. for about 5 hours in air containing about 10% by
volume of H.sub.2O.
Description
TECHNICAL FIELD
[0001] The disclosure relates to formed ceramic substrates, and
compositions thereof. In various embodiments of the disclosure, the
formed ceramic substrates may be used as a support for catalysts.
In further embodiments, the chemical composition of the formed
ceramic substrates may have a low level of chemical interaction
with said catalysts.
BACKGROUND
[0002] Formed ceramic substrates, including but not limited to high
surface area structures, may be used in a variety of applications.
Such formed ceramic substrates may be used, for example, as
supports for catalysts for carrying out chemical reactions or as
sorbents or filters for the capture of particulate, liquid, or
gaseous species from fluids such as gas streams and liquid streams.
As a non-limiting example, certain activated carbon bodies, such
as, for example, honeycomb-shaped activated carbon bodies, may be
used as catalyst substrates or for the capture of heavy metals from
gas streams.
[0003] Currently, little attention is paid to the chemical
composition of formed ceramic substrates, such as cordierite and
aluminum titanate based products, as no chemical interactions have
been reported. Many current products aim for high porosity for the
integration of selective catalytic reduction (SCR) catalysts.
However, at least some of these products show undesirable impurity
ranges, and interactions have been reported, such as, for example,
with metal-based catalysts. Thus, there is a need in the art to
prepare formed ceramic substrates that are compatible with a
broader range of SCR catalysts.
SUMMARY
[0004] In accordance with various exemplary embodiments of the
disclosure, a formed ceramic substrate is disclosed. In at least
certain embodiments, the formed ceramic substrate comprises an
oxide ceramic material. The formed ceramic substrates disclosed
herein may, in at least certain exemplary embodiments, allow for
catalytic activity to be substantially maintained. In various
exemplary embodiments, the formed ceramic substrates comprise a low
elemental alkali or alkaline earth metal content, such as, for
example, less than about 1400 parts per million ("ppm"), less than
about 1200 ppm, or less than about 1000 ppm. In other exemplary
embodiments, the formed ceramic substrates comprise a low elemental
alkali metal content, such as, for example, less than about 1000
ppm, less about 800 ppm, less than about 750, less than about 650
ppm, or less than about 500 ppm. In other exemplary embodiments,
the formed ceramic substrates comprise a low sodium content, such
as, for example, less than about 1000 ppm, less about 800 ppm, less
than about 750, less than about 650 ppm, or less than about 500
ppm. In further exemplary embodiments, the oxide ceramic material
is chosen from at least one of a cordierite phase, an aluminum
titanate phase, and fused silica. In certain embodiments, the oxide
ceramic material is a cordierite/mullite/aluminum titanate ("CMAT")
composition.
[0005] As used herein, "an elemental alkali or alkaline earth metal
concentration of less than about 1400 ppm" indicates less than
about 0.14 wt % total alkali or alkaline earth metal, wherein
alkali or alkaline earth metal includes any of lithium, sodium,
potassium, rubidium, caesium, francium, beryllium, calcium,
strontium, barium, and radium. As used herein, "an elemental alkali
metal concentration of less than about 1000 ppm" indicates less
than about 0.10 wt % total alkali metal, wherein alkali metal
includes any of lithium, sodium, potassium, rubidium, caesium, and
francium.
[0006] According to yet further exemplary embodiments are disclosed
composite bodies, and methods of preparing composite bodies, having
a substantially maintained catalytic activity. In certain
embodiments, a method of preparing a composite body having a
substantially maintained BET surface area after thermal aging
comprises the steps of providing a formed ceramic substrate
prepared from a substrate composition comprising an
oxide-containing ceramic-forming material, wherein the batch
components of the substrate composition are chosen such that the
content of elemental alkali or alkaline earth metal in the formed
ceramic substrate is less than about 1400 ppm, and applying at
least one catalyst to the formed ceramic substrate. In certain
embodiments, the batch components of the substrate composition are
chosen such that the content of elemental alkali metal in the
formed ceramic substrate is less than about 1200 ppm or less than
about 1000 ppm. In certain other embodiments, the batch components
of the substrate composition are chosen such that the content of
elemental sodium in the formed ceramic substrate is less than about
1200 ppm or less than about 1000 ppm. In certain embodiments, the
oxide-containing ceramic-forming material is chosen from a
cordierite phase, an aluminum titanate phase, and fused silica. In
yet further exemplary embodiments, the oxide ceramic material is a
CMAT composition.
[0007] In accordance with various embodiments of the invention, the
substrate composition disclosed herein may have a high porosity,
such as a porosity greater than about 55%.
[0008] In accordance with various other embodiments of the
disclosure, the composite body disclosed herein has a low
coefficient of thermal expansion, such as a coefficient of thermal
expansion less than about 3.times.10.sup.-6/.degree. C. from about
25.degree. C. to about 800.degree. C.
[0009] Both the foregoing general summary and the following
detailed description are exemplary only and are not restrictive of
the disclosure. Further features and variations may be provided in
addition to those set forth in the description. For instance, the
disclosure describes various combinations and subcombinations of
the features disclosed in the detailed description. In addition, it
will be noted that where steps are disclosed, the steps need not be
performed in that order unless explicitly stated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a bar graph showing the value of the determination
coefficient, R.sup.2, between the copper chabazite ("Cu/CHA")
zeolite surface area loss after thermal aging and the concentration
of each of the individual elements in a cordierite ceramic with
which the zeolite was admixed. The correlation between surface area
loss and sodium content of the ceramic indicates the desirability
of maintaining a low sodium content in the formed ceramic substrate
in order to maintain high BET surface area, i.e., high catalytic
activity after thermal aging.
[0011] FIG. 2 shows percent BET surface area loss in Cu/CHA zeolite
after thermal aging versus concentration of sodium in a cordierite
ceramic powder with which the zeolite was admixed. Rectangular
regions delineate certain embodiments of the disclosure, wherein
the sodium concentration in the ceramic is less than about 1000
ppm, less than about 800 ppm, less than about 650 ppm, and less
than about 500 ppm. The open circle denotes zeolite that was aged
in the absence of a ceramic powder.
[0012] FIG. 3 is a bar graph showing the concentration of each of
the individual elements in three aluminum titanate ceramic
examples.
[0013] FIG. 4A is a graph illustrating NO conversion as a function
of reaction temperature.
[0014] FIG. 4B is a bar graph illustrating NO conversion efficiency
at 350.degree. C. for the compositions C1 and C2 relative to the
reference composition.
[0015] FIG. 5 is a bar graph illustrating XRD Rietveld results for
fresh and thermally aged CuCHA/AT HP compositions.
[0016] FIG. 6 is a scanning electron micrograph showing a region of
sodium-containing glass (dark pocket) adjacent to copper-containing
zeolite catalyst (bright area).
[0017] FIG. 7 is a graph showing the concentration of CuO in a
SAPO-34 zeolite washcoat versus the concentration of Na.sub.2O in
the same zeolite washcoat for examples C1 and C2, aged at 600 or
800.degree. C. for 5 hours, as determined by electron probe
microanalysis of various locations within the samples. Also shown
for comparison is the concentration of CuO in the SAPO-34 zeolite
washcoat before thermal aging in the presence of a ceramic
substrate, and the projected composition of the same zeolite
washcoat after complete exchange of sodium for copper.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0018] According to one exemplary embodiment, formed ceramic
substrates having an elemental alkali or alkaline earth metal
concentration of less than about 1400 ppm are disclosed. According
to another exemplary embodiment, formed ceramic substrates having
an elemental alkali metal concentration of less than about 1000 ppm
are disclosed. In certain embodiments, the formed ceramic
substrates have an elemental sodium concentration of less than
about 1000 ppm. As used herein, "an elemental sodium concentration
of less than about 1000 ppm" indicates less than about 0.10 wt %
Na, or less than about 0.13% Na.sub.2O. In various embodiments, the
formed ceramic substrates may have a porosity of at least about
50%, such as at least about 60%.
[0019] In certain exemplary embodiments, the formed ceramic
substrate is comprised predominantly of a cordierite phase, an
aluminum titanate phase, or fused silica. In yet further exemplary
embodiments, the formed ceramic substrate predominantly comprises a
CMAT composition. As used herein, the term "predominantly" means at
least about 50% by weight, such as at least about 60%, at least
about 70%, or at least about 75%, by weight. The percent by weight
can be measured as a percentage by weight of the total crystalline
phases of the formed ceramic substrate. This percentage may be
measured by any means known to those skilled in the art, such as,
for example, by Rietveld x-ray diffractometry.
[0020] In yet further embodiments, the formed ceramic substrate may
comprise a catalyst. For example, the formed ceramic substrate may
be coated with a zeolite catalyst such as a copper-containing
zeolite, for example Cu/CHA, and may be a composite body. Such a
composite body may be useful, as non-limiting examples, as an
exhaust gas particulate filter or substrate such as for vehicles
powered by diesel or gasoline internal combustion engines. In
various non-limiting embodiments, the composite body may be in the
form of a honeycomb body.
[0021] It has been found that, depending upon the zeolite type,
interaction between the ceramic substrate material, such as a
cordierite or aluminum titanate substrate material, and a zeolite
catalyst can occur during typical aging conditions, such as
exposure to elevated temperatures, e.g. greater than about
700.degree. C., and hydrothermal conditions, e.g. water vapor
present at about 1-15%. The low alkali or alkaline earth metal
content of the formed ceramic substrate compositions disclosed
herein may result in a reduced interaction with zeolite catalysts,
for example Cu/CHA zeolites, under such typical thermal aging
conditions, in at least certain embodiments.
[0022] Accordingly, the alkali metal content of the formed ceramic
substrate in certain embodiments disclosed herein may be less than
about 1000 ppm, such as less than about 800 ppm, less than about
650 ppm, or less than about 500 ppm. In certain embodiments, the
elemental sodium content of the formed ceramic substrate may be
less than about 1000 ppm, such as less than about 800 ppm, less
than about 650 ppm, or less than about 500 ppm. In further
exemplary embodiments, the sum of the sodium plus other elemental
alkali or alkaline earth metal contents in the formed ceramic
substrate may be less than about 1400 ppm (expressed as the
elements), for example less than about 1200 ppm, 1000 ppm, or less
than about 700 ppm.
[0023] In at least certain exemplary embodiments, the porosity of
the formed ceramic substrate may be at least about 55%, such as,
for example, at least about 58%, at least about 60%, at least about
62%, at least about 64%, at least about 65%, or at least about 66%.
Increased porosity may be beneficial in accommodating large amounts
of catalyst within the porous walls of the formed ceramic
substrate, for example in a honeycomb wall-flow filter, while
maintaining a low pressure drop.
[0024] A large median pore diameter may also help to maintain a low
pressure drop, for example in a catalyzed wall-flow filter. In
certain embodiments, the median pore diameter of the formed ceramic
substrate may be at least about 10 .mu.m, such as, for example at
least about 12 .mu.m, at least about 15 .mu.m, at least about 17
.mu.m, at least about 18 .mu.m, at least about 22 .mu.m, or at
least about 24 .mu.m.
[0025] The pore size distribution of the formed ceramic substrate
may satisfy the condition that d.sub.f, defined as
(d.sub.50-d.sub.10)/d.sub.50, is less than about 0.50, such as for
example less than about 0.45, less than about 0.40, or less than
about 0.35. In certain exemplary embodiments, the d.sub.f is less
than about 0.2, such as about 0.16. This is because small values of
d.sub.f tend to correlate with minimal penetration of soot into the
walls of the formed ceramic substrate which would otherwise tend to
increase pressure drop. In certain embodiments, the pore size
distribution may also satisfy the condition that d.sub.b, defined
as (d.sub.90-d.sub.10)/d.sub.50, is less than about 2.0, such as,
for example, less than about 1.8, less than about 1.5, or less than
about 1.25. In other exemplary embodiments, d.sub.b is less than
about 1.0, such as, for example, less than about 0.9, less than
about 0.5, or less than about 0.4. Low values of d.sub.b imply
fewer large pores, which may reduce the strength of the formed
ceramic substrate and, in certain embodiments, the filtration
efficiency of the filter. The values of d.sub.10, d.sub.50, and
d.sub.90 are the pore diameters at which about 10%, 50%, and 90%,
respectively, of the pores are of a smaller diameter on a pore
volume basis, and pore diameter and % porosity may be measured, for
example, on the bulk formed ceramic by mercury porosimetry.
[0026] As used herein, the term modulus of rupture (MOR) is the
modulus of rupture of the formed ceramic substrate, as measured by
the four-point method on a cellular ceramic bar whose length is
parallel to the direction of the channels. The term closed frontal
area (CFA) refers to the closed frontal area fraction of the formed
ceramic substrate, that is, the fraction of area occupied by the
porous ceramic walls in a cross section taken perpendicular to the
direction of the channels.
[0027] In certain embodiments according to the disclosure, the
value of MOR/CFA may be at least about 125 psi, such as, for
example, at least about 200 psi, at least about 300 psi, or at
least about 400 psi. In other exemplary embodiments, the value of
MOR/CFA may be at least about 500 psi, such as, for example at
least about 800 psi, at least about 1000 psi, at least about 1200
psi, at least about 1400 psi, or at least about 1600 psi. The CFA
may be computed from the relation:
CFA=(bulk density of substrate)/[(skeletal density of
ceramic)(1-P)]
where P=% porosity/100. The bulk density of the substrate is
determined by measuring the mass of an approximately 0.5
inch.times.1.0 inch.times.5 inch bar of the ceramic honeycomb
substrate cut parallel to the length of the channels and dividing
by the volume of the ceramic bar (height.times.width.times.length);
the skeletal density of the ceramic is determined by standard
methods known in the art, such as by mercury porosimetry or the
Archimedes method, or may be set equal to the theoretical density
of the ceramic as computed from the crystallographic unit cell
densities of the individual phases comprising the ceramic.
[0028] For a predominantly cordierite formed ceramic substrate, the
skeletal density may be approximately 2.51 g cm.sup.-3. For a
predominantly aluminum titanate formed ceramic substrate, the
skeletal density may be range from about 3.2 g cm.sup.-3 to about
3.5 g cm.sup.-3, such as, for example, about 3.25 g cm.sup.-3. A
high value of MOR/CFA may, in certain exemplary embodiments, be
desired to provide mechanical durability during handling and use.
Moreover, a high value of MOR/CFA may enable the use of high %
porosity, large median pore size, and/or thin walls to achieve low
pressure drop when the formed ceramic substrate is used as a
filter.
[0029] In various other exemplary embodiments disclosed herein, the
strain tolerance, defined as MOR/E, of the formed ceramic substrate
may be at least about 0.10% (0.10.times.10.sup.-2), for example at
least about 0.12%, or at least about 0.14%, where E is the Young's
elastic modulus as measured by a sonic resonance technique on a
cellular bar parallel to the lengths of the channels and having the
same cell density and wall thickness as the specimen used in the
measurement of MOR. In certain other exemplary embodiments, the
strain tolerance of the formed ceramic substrate may be at least
about 0.08%, for example at least about 0.09%. A high strain
tolerance may be desirable for achieving high thermal shock
resistance.
[0030] In still other embodiments, the microcrack index, designated
"Nb.sup.3," is less than about 0.10, such as less than about 0.08,
less than about 0.06, or less than about 0.04. Microcracking may
occur from residual stresses that arise during cooling of a fired
formed ceramic substrate. For example, microcracks may form and
open during cooling and close again during heating. Microcracking
may lower the thermal expansion of a formed ceramic substrate in
addition to reducing its strength. The microcrack index may be
defined by the relation
Nb.sup.3=(9/16)[(E.degree..sub.25/E.sub.25)-1], wherein
E.degree..sub.25 is the room-temperature elastic modulus of the
ceramic in a hypothetical state of zero microcracking, determined
by extrapolation to 25.degree. C., of a tangent to the curve
constructed through the elastic modulus data measured during
cooling from 1200.degree. C. A low value of Nb.sup.3 corresponds to
a low degree of microcracking.
[0031] Accordingly, the ratio of elastic modulus measured at about
800.degree. C. during heating to the initial room temperature
(25.degree. C.) elastic modulus, E.sub.800/E.sub.25, may in certain
embodiments be less than about 1.05, such as less than about 1.03,
less than about 1.00, less than about 0.98, or less than about
0.96. Low values of Nb.sup.3 and E.sub.800/E.sub.25 may correspond
to relatively low levels of microcracking, which enable greater
strength of the ceramic walls.
[0032] As used herein, a cordierite phase is defined as a phase
having the crystalline structure of orthorhombic cordierite or
hexagonal indialite, and comprised predominantly of the compound
Mg.sub.2Al.sub.4Si.sub.5O.sub.18. As used herein, an aluminum
titanate phase is defined as a phase having the crystalline
structure of pseudobrookite, and comprised predominantly of the
compounds Al.sub.2TiO.sub.5 and MgTi.sub.2O.sub.5. In certain
embodiments, the pseudobrookite comprises from about 70% to about
100% Al.sub.2TiO.sub.5. As used herein, CMAT comprises about 40% to
about 80% pseudobrookite, about 0% to about 30% cordierite, and
about 0 to about 30% mullite, where pseudobrookite is defined as
aluminum titanate or an aluminum titanate magnesium titanate solid
solution.
[0033] In certain embodiments disclosed herein, the formed ceramic
substrate predominantly comprises a pseudobrookite phase. In yet
further embodiments, the formed ceramic substrate has a combined
concentration of Na.sub.2O and K.sub.2O of less than about 0.4%,
such as, for example, less about 0.2% or less than about 0.1%,
washcoated with a zeolite catalyst such as Cu/CHA or Fe-ZSM-5, at a
washcoat loading ranging from about 20 g/L to about 200 g/L.
[0034] The value of about 0.4% by weight of sodium oxide provides
an upper limit on tolerable levels of alkali. This amount is
determined by meeting the condition that the concentration of
Na.sub.2O in mol/L in the composite body is equal to or less than
the concentration of CuO. The rational is as follows: zeolite with
a Cu concentration of about 2%, washcoated to a loading of about
120 g/L onto a formed ceramic substrate with a density of about 500
g/L. This assumes complete ion exchange of Cu.sup.2+ for 2
Na.sup.+. A lower value such as about 25%, or in certain
embodiments about 10%, of the maximum is recommended so that the
composite body maintains good SCR performance over its
lifetime.
[0035] The low alkali or alkaline earth metal formed ceramic
substrate and composite body disclosed herein are advantageous in
numerous ways. By way of example, the lifetime of a zeolite
catalyst may be extended; the zeolite catalyst may operate at
higher temperatures; the amount of catalyst required may be
reduced; and transition metal components from the catalyst are not
exchanged with components of the composite body or the formed
ceramic substrate to change the composite body or substrate
properties. Other objects and advantages of the embodiments
disclosed herein will be apparent to those of ordinary skill in the
art.
[0036] The disclosure also provides a method of making a formed
ceramic substrate having less than about 1000 ppm sodium and at
least about 55% porosity, such as at least about 60% porosity. In
certain embodiments, the method entails mixing together the
inorganic ceramic-forming raw materials with other ingredients
known in the art that may, for example, comprise organic binders,
plasticizers, lubricants, and fugitive pore formers. In certain
embodiments disclosed therein, the inorganic and organic components
may be mixed with a solvent phase to form a moldable compounded
material, which is subsequently formed into a body, such as
cellular body like a honeycomb body, by a process such as
extrusion, although other forming processes such as casting or
pressing may be used.
[0037] Also disclosed herein are batch compositions useful for
producing an oxide-containing ceramic-forming green body. In
particular, such batch compositions, when formed into green bodies
and fired, may produce ceramic articles exhibiting a low elemental
alkali or alkaline earth metal content, such as a low sodium
content. Forming or shaping of the green body from the batch
composition may be done by, for example, typical ceramic
fabrication techniques, such as uniaxial or isostatic pressing,
extrusion, slip casting, and injection molding. Extrusion, for
example, may be used when the formed ceramic substrate is of a
honeycomb geometry, such as for a catalytic converter flow-through
substrate or a diesel particulate wall-flow filter.
[0038] The batch components and solvents for forming the batch
composition may be selected such that the mass of alkali or
alkaline earth metal contributed by the organic and inorganic
constituents of the batch and the solvents, divided by the mass of
the inorganic constituents of the batch, is less than about 1000
ppm, as expressed in the following equation:
{.SIGMA.[(m.sub.i)(w.sub.am,i)]+.SIGMA.[(m.sub.o)(w.sub.am,o)]+.SIGMA.[(-
m.sub.s)(w.sub.am,s)]}/.SIGMA.[(m.sub.i)]<1.times.10.sup.-3
where m.sub.i, m.sub.o, and m.sub.s represent the mass (part by
weight) of each inorganic, organic, and solvent component of the
batch, respectively, and w.sub.am,i, w.sub.am,o, and w.sub.am,s
represent the weight fractions of alkali or alkaline earth metal
(expressed as the element) in each respective inorganic, organic,
and solvent component.
[0039] The resulting green body may then be dried and fired to a
temperature sufficient to remove the organic components, including
the fugitive pore formers, and to sinter the inorganic powers to
form a formed ceramic substrate. The amount of pore former material
in the batch composition may be adjusted to provide the desired
porosity, for example a porosity of at least about 60%. The
particle size distributions of the inorganic and pore former
materials may be selected by those of ordinary skill in the art to
achieve the desire pore size distribution.
[0040] The resulting green bodies can be optionally dried, and then
fired in a gas or electric kiln or by microwave heating, under
conditions effective to convert the green body into a formed
ceramic substrate. For example, the firing conditions effective to
convert the green body into a formed ceramic substrate can comprise
heating the green body at a maximum soak temperature in the range
of from about 1250.degree. C. to about 1450.degree. C., such as
from about 1300.degree. C. to about 1350.degree. C., and
maintaining the maximum soak temperature for a hold time sufficient
to convert the green body into a formed ceramic substrate, followed
by cooling at a rate sufficient not to thermally shock the sintered
article.
[0041] In certain other embodiments, the green body may be fired in
multiple firing steps. For example, in certain methods of firing,
the green body containing batch materials may be heated between
room temperature and a top soak temperature, during which organics
are removed from the green body and the resultant phases are
formed. The firing conditions may be chosen such that the body does
not undergo stresses exceeding its strength, providing a resultant
body that is crack-free. Various firing cycles for different
materials are well known in the art.
[0042] When the ceramic is chosen from a cordierite ceramic or an
aluminum titanate ceramic, for example, raw materials may comprise,
for example, titanium dioxide, talc, calcined talc, magnesium
oxide, magnesium hydroxide, magnesium carbonate, magnesium
aluminate spinel, alpha-alumina, boehmite, kaolin, calcined kaolin,
quartz, fused silica, and other additives that are well known in
the art. Aluminum trihydrate may be used, but should be selected
from special sources of aluminum trihydrate having a lower sodium
content than is typical of many commercially available aluminum
trihydrate powders. Magnesium sources may contain less than about
0.30 wt % calcium oxide.
[0043] The organic binders and forming aids disclosed herein may
include a methyl cellulose binder and a stearic acid lubricant.
Sodium stearate, although known in the art as an organic lubricant,
has a high concentration of sodium and thus may not be suitable for
certain embodiments disclosed herein.
[0044] The pore former materials disclosed herein may include
organic particulates possessing a low ash content, such as, for
example, graphite, starch, nut shell flour, hard waxes, and other
pore former materials known in the art. Starches may include any
starch known in the art, such as cross-linked, native, and modified
starches, including for example pea starches, potato starches, corn
starches, and sago starches.
[0045] In certain embodiments disclosed herein, the raw materials
envisioned for use in the formed ceramic substrate may be washed or
chemically cleaned to lower their alkali or alkaline earth metal
content to an amount suitable for use in the formed ceramic
substrates disclosed herein.
[0046] Table A below shows exemplary alkali and alkaline earth
metal contents for various known raw materials.
TABLE-US-00001 TABLE A Element, ppm Component Na K Ca Inorganics
Alumina, Microgrit .RTM. WCA25 3400 20 230 Alumina, Almatis .RTM.
ACG15 800 10 210 Titania, TiPure R101 130 1 0 Titania, Hitox .RTM.
STD 1800 0 110 Talc, Cercron .RTM. MB 96-67 300 40 1100 Mg(OH)2,
Magshield .RTM. UF 29 7 4074 Silica, Microsil .RTM. 4515 40 60 53
Y.sub.2O.sub.3 50 20 na CeO.sub.2, PIDC 38 18 100 Pore Formers
Graphite, Ashbury 4566 200 20 210 Native potato starch, Emsland 30
900 106 VHXL Potato Starch, Emsland F8684 2500 180 94 VHXL Potato
Starch, Emsland F8684O 230 26 320 VHXL Emselect 1000, Emsland
F10153 570 63 480 Bylina pea starch 73 31 140 XL pea starch,
Emsland F9694 390 20 145 VHXL pea starch, Emsland F10157 230 11 140
XL Sago, Ingredion .RTM. E910-55 55 6 240 Polyethylene, Honeywell
ACumist .RTM. F45 2 1 9 Extrusion Aids Fatty Acid na na na Binder:
F240 3500 50 na Binder: TY11A 2100 20 na
[0047] As used in the present disclosure, the term "formed
substrate," and variations thereof, is intended to include ceramic,
inorganic cement, and/or carbon-based bodies. Formed ceramic
substrates include, but are not limited to, those comprised of
cordierite, aluminum titanate, and fused silica. Inorganic cement
substrates include, but are not limited to, those comprised of
inorganic materials comprised of an oxide, sulfate, carbonate, or
phosphate of a metal, including calcium oxide, calcium aluminate
cements, calcium/magnesium sulfate cements, and calcium phosphate.
Carbon-based materials include, but are not limited to, synthetic
carbon-based polymeric material (which may be cured or uncured);
activated carbon powder; charcoal powder; coal tar pitch; petroleum
pitch; wood flour; cellulose and derivatives thereof; natural
organic materials, such as wheat flour, wood flour, corn flour,
nut-shell flour; starch; coke; coal; or mixtures thereof.
[0048] After preparation of the formed ceramic substrate, a
catalyst composition may be added to the formed ceramic substrate
in order to prepare a composite body. Composite bodies may have
various uses, including, for example, as filters. A catalyst may be
applied to the formed ceramic substrate in any way known in the
art, including, for example, by washcoating the formed ceramic
substrate with a catalyst. A catalyst may also be incorporated into
the formed ceramic substrate as part of the batch composition to
form a composite body.
[0049] In certain embodiments disclosed herein, the composite body
undergoes thermal aging but still substantially maintains catalyst
activity. In certain embodiments, catalytic activity may be
measured by the nitric oxide conversion efficiency of the thermally
aged composite body at a given temperature, such as, for example,
at least about 200.degree. C., such as at least about 350.degree.
C. In certain embodiments disclosed herein, the nitric oxide
conversion efficiency may be greater than about 80%, such as
greater than about 90%, or greater than about 95%.
[0050] As discussed above, a reduction in catalyst surface area on
a substrate correlates to a reduction in its catalytic activity;
likewise, the greater the percentage of BET surface area that can
be maintained, the greater the catalytic activity that is
maintained. For example, in certain embodiments, the composite body
will maintain a BET surface area of at least about 55% after
thermal aging. As used herein a substantially maintained BET
surface area means a BET surface area retention of at least about
55%, such as at least about 60% or at least about 70%.
[0051] In other embodiments disclosed herein, thermal degradation
of the composite body may not be solely responsible for the loss in
filter efficiency observed at high alkali and alkaline earth metal
concentrations. In accordance with certain embodiments disclosed
herein, alkali and alkaline earth metal impurities may partition in
the glass phase of the formed ceramic substrate, thus having a high
mobility. It is theorized that solid-state ion exchange may take
place between the formed ceramic substrate, where the alkali or
alkaline earth metal in the glass phase is highly mobile, and the
metal ions located in the catalyst, such as the copper in a Cu/CHA
zeolite catalyst. The ion exchange may be stoichiometric.
[0052] The loss in active metal catalyst sites may be explained by
a stoichiometric ion exchange between the alkali and alkaline earth
metal ions located in the glass phase of the formed ceramic
substrate and the metal ions located in the catalyst, as may be
evidenced, for example, by microprobe analysis. Furthermore, the
ion exchange may be a function of the initial alkali or alkaline
earth metal oxide content in the formed ceramic substrate.
Therefore, in certain embodiments according to the disclosure,
there is a maximum acceptable limit for alkali or alkaline earth
metal oxide concentration the formed ceramic substrate to minimize
ion exchange reactions between the formed ceramic substrate and the
active catalyst phase, thereby minimizing catalyst degradation
under mild thermal aging conditions.
[0053] Thermal aging conditions used may include typical aging
conditions known to those skilled in the art. In certain
embodiments, the thermal aging conditions may include exposure to
elevated temperatures, such as temperatures greater than about
700.degree. C., and hydrothermal conditions, such as water vapor
present in an amount ranging from about 1% to about 15%. In certain
embodiments, thermal aging may be conducted in air at a constant
flow rate of about 200 scfm and containing air with about 10%
moisture, and heating the sample inside a furnace to about
800.degree. C. for a sufficient amount of time. In certain
embodiments, thermal aging may include a pre-conditioning step,
such as pre-conditioning the sample at about 600.degree. C. for
about 5 hours in air with about 10% moisture.
[0054] Various reactors may be available to thermally age mixtures
of catalyst powder, such as Cu/CHA catalyst powder and pulverized
ceramic substrate in order to subsequently ascertain catalytic
activity. Any reactor known in the art may be used. In certain
embodiments, for example, air may flow through a mass flow
controller (MFC) before proceeding into a humidifier. From the
humidifier, the air then cycles through deionized water into a
water pump and back into the humidifier. The air then flows through
a tube furnace containing a vent at the end opposite the
humidifier. The furnace further contains a sample, for example a
sample comprising mixtures of catalyst powder and pulverized
ceramic substrate, wherein the sample is contained between two
pieces of quartz wool. The reactor functions to thermally age the
sample as described above.
[0055] Also disclosed herein is a method of using a Cu/CHA zeolite
coated substrate as a filter for the reduction of nitric oxide
(NO.sub.x) and other gaseous and particulate matter, wherein the
product filter demonstrates superior filtering capabilities.
[0056] It is well within the ability of those skilled in the art to
choose oxide-containing ceramic-forming material, pore former,
solvent and other excipients to yield a formed ceramic substrate,
such as a cordierite, aluminum titanate or fused silica body,
having the desired properties.
[0057] Unless otherwise indicated, all numbers used in the
specification and claims are to be understood as being modified in
all instances by the term "about," whether or not so stated. It
should also be understood that the precise numerical values used in
the specification and claims form additional embodiments of the
disclosure. Efforts have been made to ensure the accuracy of the
numerical values disclosed in the Examples. Any measured numerical
value, however, can inherently contain certain errors resulting
from the standard deviation found in its respective measuring
technique.
[0058] As used herein the use of "the," "a," or "an" means "at
least one," and should not be limited to "only one" unless
explicitly indicated to the contrary.
[0059] It is to be understood that both the foregoing general
description and the detailed description are exemplary and
explanatory only and are not intended to be restrictive.
[0060] The accompanying drawings, which are incorporated in and
constitute a part of this specification, are not intended to be
restrictive, but rather illustrate embodiments of the
disclosure.
[0061] Other embodiments will be apparent to those skilled in the
art from consideration of the specification and practice of the
disclosure.
EXAMPLES
[0062] The following examples are not intended to be limiting of
the disclosure.
Example 1
Cordierite Substrate
[0063] In an effort to discover the chemical and/or physical
properties of a cordierite honeycomb ceramic substrate that
influence the retention of surface area of a Cu/CHA zeolite
catalyst with which it is in contact, a large number of different
cordierite samples spanning a range in chemical composition of
minor metal oxide constituents, % porosity, and % glass, were
selected. Each ceramic was crushed into a powder and mixed with a
Cu/CHA zeolite catalyst powder in a weight ratio of about 4:1.
Approximately 1.25 grams of the mixture was placed in a small
reactor.
[0064] The thermal aging test was conducted in air at a constant
flow rate of 200 scfm and containing 10 vol. % of water. The sample
was heated inside the furnace to 800.degree. C. for 64 hours. This
thermal cycle is meant to simulate aging of the catalyst in an
SCR-on-DPF application. After exposure in the furnace, the BET
surface area of the aged mixture was measured using the nitrogen
adsorption technique, and the BET surface area of the zeolite
component of the mixture was computed from the value obtained for
the zeolite plus substrate mixture, assuming the surface area
contribution from the ceramic phase to be negligible. Reference
measurements were also made with the fresh zeolite catalyst as well
as with the zeolite catalyst aged without the presence of a
substrate material.
[0065] The chemical compositions of the different cordierite
substrates and filter materials were analyzed using ICP, and the
impurities and their amounts are provided in Table 1, along with
the % porosity as measured by mercury porosimetry. Table 1 also
provides the measured reduction in BET surface area of the zeolite.
FIG. 1 shows the value of the determination coefficient, R.sup.2,
between the surface area loss of the Cu/CHA zeolite after thermal
aging and the concentrations of each of the individual elements in
the co-mixed ceramic. The surface area reduction of the Cu/CHA
zeolite was discovered to have a strong correlation with the sodium
(Na) content of the ceramic, yielding an R.sup.2 value of 83%. The
correlation between the zeolite surface area loss and the
concentration of sodium in the ceramic is shown graphically in FIG.
2. Additionally, reactivity of the substrates was found to have a
weaker correlation with the Ca and P concentrations in the
ceramics.
[0066] Table 2 lists the chemical compositions, in weight
percentages of the oxides, of raw materials used in the fabrication
of Comparison Examples 12 and 18 and Inventive Examples 4, 6, and
7. It can be seen that the Micral 6000 aluminum trihydrate,
cross-linked potato starch, and sodium stearate comprise
significant sources of sodium to the ceramic-forming batch.
[0067] Table 3 lists the weight percentages of the raw materials
used for Comparison Examples 12 and 18 and Inventive Examples 4, 6,
and 7.
[0068] Table 4 lists additional details on the physical properties
of Comparison Examples 12 and 18 and Inventive Examples 4, 6, and
7.
[0069] The use of sodium stearate, a high-sodium aluminum
trihydrate, and a high-sodium potato starch in the raw material
mixture used to form Comparative Example 18 resulted in a sodium
content in the fired ceramic body of 2900 ppm. This high sodium
concentration in the ceramic resulted in an 89% surface area loss
of the Cu/CHA zeolite in a powder mixture with the ceramic after
the thermal aging treatment.
[0070] The replacement of sodium stearate by stearic acid in
Comparative Example 12 resulted in a reduction in sodium
concentration in the fired ware to 1900 ppm. The surface area loss
in the Cu/CHA after thermal aging was reduced to 55%, but was still
undesirably high.
[0071] Inventive Example 6 utilized the same raw materials as
Comparative Example 12 except that the high-sodium aluminum
trihydrate was replaced with lower-sodium alpha-alumina. The sodium
content of the fired body was thereby further reduced to 840 ppm,
and the surface area loss of the Cu/CHA zeolite after thermal aging
was decreased to only 38%. A porosity of 64% and a narrow pore size
distribution provide a pore microstructure capable of maintaining a
low filter pressure drop even with a high loading of zeolite
catalyst in the pores of the filter walls.
[0072] Inventive Examples 4 and 7 illustrate the use of other
low-sodium raw materials to achieve fired ceramic substrates having
less than about 1000 ppm sodium, thereby preserving a useful
surface area and activity in the Cu/CHA zeolite catalyst in contact
with the ceramic. Examples 4 and 7 further illustrate ceramics
having greater than about 60% porosity and narrow pore size
distribution, but with finer median pore diameters that allow high
filtration efficiency to be maintained in filters having thinner
walls.
[0073] Table 1 shows percent loss in BET surface area of zeolite
after thermal aging, alone (Ex. 1) and mixed with cordierite
ceramic powders (Ex. 2-19), and % porosity and concentrations of
minor and trace elements in ceramics. Asterisks indicate inventive
examples.
[0074] Table 2 shows the chemical compositions of raw materials
used in selected examples 4, 6, 7, 12, and 18 of Table 1 (weight
percentages).
TABLE-US-00002 TABLE 1 % Surface Area Ex. No. Loss Na Ba Ca Ce Co
Cr Fe K La 1 2 0 0 0 0 0 0 0 0 0 (Cu/CHA) 2 10 430 46 620 47 3.4 45
2800 240 23 3 18 580 27 540 20 2.7 22 3100 240 8.7 4 30 690 18 --
10 1.4 28 170 230 1400 6 38 840 14 430 5.3 49 200 7200 150 4.5 7 38
880 20 -- 11 20 160 330 1200 8.4 8 51 1500 9.7 330 6.4 46 200 7200
110 2.6 9 64 1500 9.7 330 6.4 46 200 7200 110 2.6 10 70 1500 16 650
15 2.4 28 3500 510 7 11 85 1800 11 420 7.5 44 210 7100 230 3.1 12
55 1900 16 460 6.1 47 230 7100 250 4.8 13 92 2100 32 790 12 2.2 33
2500 240 7 14 90 2200 14 450 33 59 180 8000 120 4.6 15 93 2200 21
610 20 19 24 2600 110 11 16 86 2300 25 980 1 1.8 28 2600 810 1300
17 94 2500 42 1100 1.6 24 150 3900 310 1400 18 89 2900 18 460 6.2
48 250 6800 290 4.8 19 95 3800 45 1600 4 26 160 4100 370 2300 %
Porosity in Ex. No. Mn Ni P Sr Ti V Y Zn Zr ceramic 1 0 0 0 0 0 0 0
0 0 -- (Cu/CHA) 2 27 14 200 43 3900 73 3.6 6.1 34 35 3 38 17 130 35
1400 32 73 6.1 24 -- 4 26 16 220 66 1400 43 5.9 7.2 27 61 6 19 1500
210 70 1200 27 4300 11 40 66 7 32 620 200 66 1400 53 8500 10 36 66
8 17 1400 30 3.8 1000 21 3.2 16 31 47 9 17 1400 30 3.8 1000 21 3.2
16 31 47 10 24 39 210 6.7 1500 31 4000 12 28 66 11 21 1400 180 4.8
990 23 3900 16 33 65 12 20 1400 260 81 1400 34 5300 21 42 68 13 32
59 350 55 1000 33 7.9 7.8 53 66 14 24 1200 230 4.9 910 27 4500 19
54 63 15 27 16 1300 8.7 1200 38 1.9 6.4 23 64 16 34 70 110 45 1200
31 0 5.1 19 63 17 54 800 320 49 1100 32 1.2 18 42 68 18 20 1500 260
78 1400 36 4900 24 38 65 19 54 850 600 140 1300 41 3 19 60 68
TABLE-US-00003 TABLE 2 MgO Al.sub.2O.sub.3 SiO.sub.2
Fe.sub.2O.sub.3 TiO.sub.2 Na.sub.2O K.sub.2O CaO NiO
Cr.sub.2O.sub.3 P.sub.2O.sub.5 FCOR Talc 30.14 0.19 60.60 2.32 0.00
0.010 0.00 0.120 0.48 0.00 0.00 Luzenac Jetfil 500 Talc 30.13 0.19
59.40 2.55 0.000 0.010 0.000 0.230 0.45 0.12 0.00 Magshield UF
Magnesium Hydroxide 68.21 0.09 0.29 0.140 0.006 0.000 0.000 0.760
0.00 0.00 0.00 A10 Alumina 0.00 99.90 0.036 0.014 0.00 0.015 0.005
0.033 0.00 0.00 0.00 HVA Alumina 0.00 99.90 0.008 0.014 0.00 0.067
0.005 0.010 0.00 0.00 0.00 Boehmite 0.00 79.99 0.00 0.000 0.000
0.004 0.005 0.000 0.00 0.00 0.00 Micral 6000 Aluminum Trihydrate
0.002 64.90 0.006 0.005 0.00 0.202 0.001 0.024 0.00 0.00 0.00
CHC-94 Kaolin 0.07 38.18 45.10 0.210 0.990 0.070 0.040 0.050 0.00
0.00 0.05 Cerasil 300 Quartz 0.002 0.055 99.87 0.014 0.006 0.042
0.008 0.005 0.00 0.00 0.00 Imsil A25 Quartz 0.008 0.260 99.52 0.047
0.018 0.076 0.042 0.009 0.00 0.00 0.019 Cross-Linked Potato Starch
0.003 0.00 0.005 0.00 0.00 0.270 0.020 0.014 0.00 0.00 0.087 Rice
Starch 0.013 0.00 0.012 0.00 0.00 0.116 0.016 0.002 0.00 0.00 0.099
Walnut Shell Flour 0.040 0.00 0.015 0.00 0.00 0.002 0.002 0.154
0.00 0.00 0.032 4602 Graphite 0.00 0.047 0.092 0.500 0.019 0.00
0.00 0.025 0.00 0.00 0.00 4014 Graphite -- -- -- -- -- -- -- -- --
-- -- Sodium Stearate 0.00 0.00 0.00 0.00 0.00 10.11 0.00 0.00 0.00
0.00 0.00 Stearic Acid -- -- -- -- -- -- -- -- -- -- -- Durasyn 162
Polyalphaolefin -- -- -- -- -- -- -- -- -- -- -- Tall Oil -- -- --
-- -- -- -- -- -- -- -- Methyl Cellulose 0.004 0.00 0.001 0.00 0.00
0.004 0.00 0.00 0.00 0.00 0.00
TABLE-US-00004 TABLE 3 Raw material combinations used in selected
examples of Table 1 18 12 6 7 4 Raw Material Comp. Comp. Inv. Inv.
Inv. Luzenac FCOR Talc 38.52 38.52 42.80 -- -- Luzenac Jetfil 500
Talc -- -- -- 14.35 -- Magshield UF Magnesium -- -- -- 12.00 18.77
Hydroxide A10 Aumina 12.27 12.27 12.27 -- -- HVA Alumina -- --
15.61 26.23 28.87 Boehmite -- -- -- -- 5.00 Micral 6000 Aluminum
Tri- 20.99 20.99 -- -- -- hydrate CHC-94 Kaolin 12.84 12.84 12.84
16.00 -- Cerasil 300 Quartz 15.38 15.38 16.48 -- -- Imsil A25
Quartz -- -- 31.42 47.36 Cross-Linked Potato Starch 22.00 22.00
22.00 -- -- Rice Starch -- -- -- -- 15.00 Walnut Shell Flour -- --
-- 30.00 -- 4602 Graphite 22.00 22.00 22.00 15.00 -- 4014 Graphite
-- -- -- -- 15.00 Methyl Cellulose 7.00 7.00 7.00 6.00 6.00 Sodium
Stearate 1.00 -- -- -- -- Stearic Acid -- 0.70 0.70 -- -- Durasyn
162 Polyalphaolefin -- -- -- 4.60 4.60 Tall Oil -- -- -- 0.60 0.60
Yttrium Oxide 0.40 0.40 0.40 1.00 -- Lanthanum Oxide -- -- -- --
1.00
TABLE-US-00005 TABLE 4 Properties of selected examples from Table 1
18 12 6 7 4 Pore Volume (ml/g) 0.7407 0.7962 0.7840 0.7439 0.6031 %
Porosity 64.6 67.5 64.4 65.6 60.8 d.sub.1 7.5 6.4 5.5 4.1 3.7
d.sub.2 8.9 9.0 6.9 4.9 4.2 d.sub.5 11.5 11.9 9.4 6.2 4.9 d.sub.10
14.0 14.8 12.6 7.6 5.7 d.sub.25 18.1 19.2 17.9 10.3 7.5 d.sub.50
22.2 23.6 23.2 12.7 9.5 d.sub.75 27.0 29.0 29.1 15.1 11.6 d.sub.90
40.4 44.8 44.1 19.7 16.8 d.sub.95 62.0 72.6 77.5 30.9 40.1 d.sub.98
122.0 144.3 166.5 94.0 141.2 d.sub.99 176.7 206.6 234.0 158.4 230.2
(d.sub.50 - d.sub.10)/d.sub.50 = d.sub.f 0.37 0.37 0.46 0.40 0.40
(d.sub.90 - d.sub.50)/d.sub.50 = d.sub.c 0.82 0.90 0.90 0.55 0.78
(d.sub.90 - d.sub.10)/d.sub.50 = d.sub.b 1.19 1.27 1.36 0.95 1.17
CTE.sub.25-800 (10.sup.-7/.degree. C.) 13.6 -- 13.4 15.9 14.4
CTE.sub.200-1000 (10.sup.-7/.degree. C.) 17.6 -- 17.3 20.5 19.1
CTE.sub.500-900 (10.sup.-7/.degree. C.) 20.8 -- 20.6 23.1 21.5
CTE.sub.25-1000 (10.sup.-7/.degree. C.) 14.7 -- 14.3 17.6 16.1
Axial I-ratio 0.57 -- 0.59 0.63 0.53 Powder I-ratio 0.64 -- 0.65
0.64 0.64 Transverse I-ratio 0.75 -- 0.74 0.69 0.81 % Mullite 0.8
1.3 0 0 0 % Spinel 1.3 2.0 1.0 0.9 1.5 % Alumina 0 0 0 0 0 MOR
(psi) 674 -- 369 516 427 E at 25.degree. C. (10.sup.6 psi) 0.453 --
0.290 0.264 0.296 E at 800.degree. C. (10.sup.6 psi) 0.431 -- 0.278
-- 0.280 E at 900.degree. C. (10.sup.6 psi) 0.427 -- 0.270 0.243
0.272 E at 1000.degree. C. (10.sup.6 psi) 0.430 -- 0.277 0.217
0.246 E(800)/E(25) 0.951 -- 0.959 -- 0.946 E(900)/E(25) 0.943 --
0.931 0.920 0.919 E(1000)/E(25) 0.949 -- 0.955 0.822 0.831
Microcrack Index, Nb.sup.3 0.037 -- 0.045 0.006 0.018 Bulk Density
(g cm.sup.-3) 0.372 -- 0.363 0.326 0.284 Closed Frontal Area
Fraction, CFA 0.418 -- 0.406 0.377 0.288 MOR/CFA (psi) 1610 -- 908
1369 1482 E/CFA (10.sup.6 psi) 1.08 -- 0.714 0.700 1.03 MOR/E
0.149% -- 0.127% 0.196% 0.144% TSP.sub.500 = 715 -- 619 846 671
MOR/[(E)(CTE.sub.500-900)] (.degree. C.) TSL.sub.500 = TSP.sub.500
+ 500 (.degree. C.) 1215 -- 1119 1346 1171 TSP.sub.200 = 844 -- 736
956 756 MOR/[(E)(CTE.sub.200-1000)] (.degree. C.) TSL.sub.200 =
TSP.sub.200 + 200 (.degree. C.) 1044 -- 936 1156 956 Measured
elemental Na (ppm) 2900 1900 840 880 690 B.E.T. Surface Area Loss
89% 55% 38% 38% 30%
Example 2
AT Substrate
[0075] Three coated aluminum titanate high-porosity (AT HP)
compositions C1, C2, and C3 were prepared containing different
alkaline oxide levels for Na.sub.2O and K.sub.2O. The AT HP
compositions were prepared in the form of cellular ceramic
honeycombs by routine extrusion processes, and their formulations
are displayed in Table 5, below.
TABLE-US-00006 TABLE 5 Exemplary aluminum titanate based filter
compositions Compositions Raw Materials C1 C2 C3 Inorganics
Aluminum Oxide - A10 -- -- 49.67 Aluminum Oxide - Microgrit WCA 25
44.18 -- -- Aluminum Oxide - SG3A -- 44.18 -- Titanium Dioxide -
TiPure R101 33.53 33.52 30.33 Talc - Cercron MB 96-67 19.10 19.10
Silica - Microsil 4515 - -200 mesh 2.71 2.71 10.31 Strontium
carbonate - Type DF -- -- 8.1 Calcium carbonate - HydroCarb-OG --
-- 1.39 Lanthanum Oxide - 5205 -- -- 0.2 Yttrium Oxide - Grade C
0.49 0.49 -- Pore formers Native Potato Starch 27.00 32 --
Cross-linked pea starch - F9492 -- -- 19 Synthetic Graphite - 4566
8.00 14 8 Binder Hydroxypropyl Methylcellulose - 3.00 3.00 3.00
TY11A Hydroxypropyl Methylcellulose - 1.50 1.50 1.50 F240 LF
Lubricants Fatty Acid, Tall Oil - L-5 1.00 1.00 1.00 Firing
Conditions Temperature (.degree. C.) 1355 1352 1427 Soak time (hr)
16 16 16 Properties Porosity (%) 54.87 60.63 57.5 Mean pore
diameter (.mu.m) 18.98 18.525 16.8 Thermal expansion coefficient to
1.05 1.06 0.28 800.degree. C. (ppm/.degree. C.)
[0076] The chemical compositions of the fired ceramics were
determined prior to catalyzation by ICP and XRF and are listed in
FIG. 3. The two compositions C1 and C2 have similar chemical
compositions except for their Na.sub.2O and K.sub.2O levels. This
is mostly due to the level of alkaline oxides provided by the
alumina used in the batch material. Table 6 provides the values for
Na.sub.2O and K.sub.2O for each sample C1, C2 and C3. In addition,
the washcoat loadings for the SCR testing of these three
compositions are displayed in Table 6 below.
TABLE-US-00007 TABLE 6 Na.sub.2O and K.sub.2O values and washcoat
loading of AT HP samples Washcoat Na.sub.2O in K.sub.2O in Sample
Load in g/L wt % wt % C1 75 2100 280 C2 79 700 230 C3 67 900 0
[0077] All samples were coated with a Cu/CHA coating located in the
porous walls of the filter material. All the data therefore also
provide an indication of the behavior of a commercial catalyst
technology under similar aging conditions. Even though the same
coating technique was used to catalyze all of the samples, the
washcoat loading varied somewhat. It was, however, considered close
enough to measure effects caused by different Na.sub.2O and
K.sub.2O levels, especially since the washcoat loadings for C1 and
C2 were very close. All samples were coated as 2.times.5.5'' cores
and were cut to a 4'' length for catalytic activity testing.
[0078] SCR Performance Data:
[0079] The SCR activity for all compositions with different
Na.sub.2O and K.sub.2O levels were measured on a lab-scale reactor
using the standard SCR reaction:
4NH.sub.3+4NO.fwdarw.4N.sub.2+6H.sub.2O. The SCR reaction
conditions were chosen in a way to have a test setup able to
measure the performance differences on the various samples. For
example, the gas compositions contained 500 ppm NO: 650 ppm
NH.sub.3 and a space velocity of 70.000 h.sup.-1 for samples in
2.times.4'' was used. The temperature range for SCR performance
evaluation used for this example was 225 to 525.degree. C.
[0080] Two thermal aging procedures were applied prior to SCR
performance testing. A pre-conditioning step at 600.degree. C./5
hours in air with 10% moisture was used prior to the initial SCR
testing. After SCR testing the samples were thermally aged at
800.degree. C./5 hours, also using air with 10% moisture, followed
by a second SCR performance test under the same conditions already
used for the "fresh" evaluation.
[0081] FIG. 4A shows absolute NO conversion efficiencies obtained
on two AT HP compositions C1 and C2 containing different levels of
Na.sub.2O and K.sub.2O. In addition, composition C3 is also shown
on FIG. 4A. For all materials, the SCR performance after
pre-conditioning and after thermal aging are shown as a function of
the reaction temperature.
[0082] The SCR performance after pre-conditioning for all samples
was considered similar, giving the measurement error and the
somewhat different washcoat loadings.
[0083] After thermal aging, the C3 and the C2 samples still show
only a minor effect of catalyst aging on SCR performance indicated
by a similar NO conversion efficiency as a function of reaction
temperature. The C1 sample shows a strong decrease in catalytic
activity in the temperature range from 200.degree. C. to
450.degree. C. FIG. 4B is a comparison of the NO conversion
efficiency relative to the composition C3 at 350.degree. C.
indicating a loss in activity for composition C1 in the range of
about 25%.
[0084] To determine the root cause for this loss in catalytic
activity, samples were prepared for XRD Rietveld analysis to
determine if this catalyst degradation was caused by a thermal
deterioration of the zeolite structure, which would then no longer
be available for NO conversion. Similar studies have also been
performed for cordierite compositions with different Na levels and
Cu-containing zeolites.
[0085] A powder mixture of 4 g filter material and 1 g dried
zeolite was carefully mixed, and part of this mixture was thermally
aged in air with 10% moisture at 800.degree. C./5 hours, similar to
the aging procedure for the samples used for the SCR performance
evaluation. After aging, both the fresh and the aged samples were
analyzed for zeolite content using XRD Rietveld refinement. The
results are shown in FIG. 5, where the relative Cu/CHA content is
compared for both the fresh and aged samples. Essentially no loss
in zeolite structure was found. Therefore, a thermal degradation of
the zeolite structure may be excluded and is probably not the root
cause for the strong loss in NO conversion efficiency observed.
[0086] Therefore, additional analysis was performed on these
samples. Microprobe studies on the SCR catalyst system were
performed after pre-conditioning (600.degree. C./5 hours in air
with 10% moisture) and thermal aging (800.degree. C./5 hours in air
with 10% moisture). All samples were analyzed for Na and Cu content
in the areas where the zeolite coating was located. FIG. 6 is a
scanning electron micrograph from the microprobe study showing a
region of sodium-containing glass (shown as the dark pocket in FIG.
6) adjacent to copper-containing zeolite catalyst (shown as the
bright area in FIG. 6).
[0087] According to earlier studies with similar ceramic materials,
sodium impurities may strongly partition in the glass phase of
these materials having a high mobility. The microprobe studies
indicate that a solid-state ion exchange took place between the
ceramic material, where the sodium in the glass phase is highly
mobile, and the copper ions located in the zeolite structure.
[0088] The results are displayed in FIG. 7. After 600.degree. C./5
hours, no ion exchange between the filter matrix and the Cu/CHA was
detected, indicated by the low sodium and the high copper content
in the zeolite phase. After thermal aging at 800.degree. C., ion
exchange took place for sample C1, containing around 2100 ppm
Na.sub.2O (higher sodium level). Sample C2, which had a much lower
Na.sub.2O level, did not show a high exchange rate between Na.sup.+
and Cu.sup.2+, after thermal aging at 800.degree. C./5 hours.
[0089] Since the exchange was stoichiometric (movement of Cu.sup.2+
tied to Na.sup.+ at 800.degree. C./5 hours), as also indicated by
FIG. 7, the C1 and C2 ceramic materials do not necessarily act as a
Cu-sink.
[0090] The deactivation of the Cu/CHA filter system as observed in
the SCR performance evaluation in the temperature range of 225 to
525.degree. C. can most likely be explained by a loss in active Cu
sites in the zeolite structure needed for SCR activity. The loss in
active Cu sites may be explained by a stoichiometric ion exchange
between Na.sup.+ ions located in the glass phase of the filter
material and the Cu.sup.2+ ions located in the zeolite structure,
as evidenced by microprobe analysis. Furthermore, the ion exchange
may be a function of the initial Na.sub.2O content in the filter
material composition. Therefore, in certain embodiments according
to the disclosure, a maximum acceptable limit for Na.sub.2O levels
is suggested in certain ceramic materials to avoid ion exchange
reactions between the filter material and the active catalyst phase
to avoid catalyst degradation under mild thermal aging
conditions.
[0091] Various compositions were prepared as shown in Tables 7 and
8 below, and the theoretical sodium and potassium contents have
been calculated for each composition.
TABLE-US-00008 TABLE 7 Na, K, Ca, Comp. Comp. Comp. Comp. Component
ppm ppm ppm Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9
Inorganics Alumina, Microgrit WCA25 3400 20 230 44.18% 44.18%
Alumina, Almatis ACG15 800 10 210 43.63% 43.90% 43.55% 44.18%
44.18% 44.18% 44.18% Titania, TiPure R101 130 1 0 33.52% 33.52%
32.93% 17.03% 33.52% 33.52% 33.52% 33.52% Titania, Hitox STD 1800 0
110 34.07% 17.46% Talc, Cercron MB 96-67 300 40 1100 19.10% 19.10%
18.83% 18.82% 18.77% 19.10% 19.10% 19.10% 19.10% Mg(OH)2, Magshield
UF 29 7 4074 Silica, Microsil 4515 40 60 53 2.71% 2.71% 2.67% 2.24%
2.23% 2.71% 2.71% 2.71% 2.71% Y2O3 50 20 na 0.49% 0.49% 0.49% 0.49%
0.49% CeO2, PIDC 38 18 100 1.93% 0.97% 0.96% 0.96% Pore Formers (as
super addition to the inorganics) Graphite, Ashbury 4566 200 20 210
8.00% 8.00% 10.00% 8.00% 10.00% 14.00% 10.00% 10.00% 14.00% Native
potato starch, Emsland 30 900 106 27.00% 27.00% 30.00% 32.00%
30.00% 32.00% VHXL Potato Starch, Emsland F8684 2500 180 94 31.50%
VHXL Potato Starch, Emsland 230 26 320 F8684O VHXL Emselect 1000,
Emsland 570 63 480 F10153 Bylina pea starch 73 31 140 XL pea
starch, Emsland F9694 390 20 145 27.00% 30.00% VHXL pea starch,
Emsland F10157 230 11 140 XL Sago, Ingredion E910-55 55 6 240
Polyethylene, Honeywell ACumist 2 1 9 F45 Extrusion Aids and
Binders (as super addition to the inorganics) Fatty Acid na na na
1.35% 1.35% 1.41% 1.35% 1.40% 1.46% 1.40% 1.40% 1.46% Binder: F240
3500 50 na 4.05% 4.05% 8.91% 2.03% 2.10% 4.38% 4.20% 4.20% 4.39%
Binder: TY11A 2100 20 na 2.03% 2.03% 4.05% 4.20% 2.19% 2.10% 2.10%
2.20% Properties Calculated Na content, ppm 0.193% 0.183% 0.159%
0.121% 0.094% 0.070% 0.068% 0.079% 0.070% Calculated K content, ppm
0.003% 0.027% 0.008% 0.026% 0.029% 0.031% 0.029% 0.002% 0.031%
Calculated Ca content, ppm 0.037% 0.036% 0.036% 0.039% 0.038%
0.037% 0.036% 0.037% 0.037% Total Calculated Na + K + Ca content,
ppm 0.233% 0.246% 0.202% 0.186% 0.161% 0.138% 0.133% 0.119% 0.138%
Porosity, % 58.0 55.4 58.1 51.6 60.7 61.5 59.6 61.2 61.7
TABLE-US-00009 TABLE 8 Na, K, Ca, Component ppm ppm ppm Ex. 10 Ex.
11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex. 19
Inorganics Alumina, Microgrit WCA25 3400 20 230 Alumina, Alnnatis
ACG15 800 10 210 44.18% 43.63% 43.76% 43.76% 43.76% 43.76% 43.76%
41.71% 43.95% 41.91% Titania, TiPure R101 130 1 0 33.52% 32.93%
33.19% 33.19% 33.19% 33.19% 33.19% 33.10% 33.14% 33.25% Titania,
Hitox STD 1800 0 110 Talc, Cercron MB 96-67 300 40 1100 19.10%
18.83% 18.92% 18.92% 18.92% 18.92% 18.92% 20.74% 9.47% 20.84%
Mg(OH)2, Magshield UF 29 7 4074 4.43% Silica, Microsil 4515 40 60
53 2.71% 2.67% 2.68% 2.68% 2.68% 2.68% 2.68% 3.01% 8.53% 3.02%
Y.sub.2O.sub.3 50 20 na 0.49% CeO.sub.2, PIDC 38 18 100 0.49% 1.93%
1.46% 1.46% 1.46% 1.46% 1.46% 1.46% 0.98% Pore Formers (as super
addition to the inorganics) Graphite, Ashbury 4566 200 20 210
10.00% 14.00% 12.00% 12.00% 12.00% 12.00% 12.00% 10.00% 14.00%
10.00% Native potato starch, 30 900 106 31.00% Emsland VHXL Potato
Starch, 2500 180 94 Emsland F8684 VHXL Potato Starch, 230 26 320
31.00% Emsland F8684O VHXL Emselect 1000, 570 63 480 31.00% Emsland
F10153 Bylina pea starch 73 31 140 31.00% XL pea starch, Emsland
390 20 145 28.50% 16.00% F9694 VHXL pea starch, Emsland 230 11 140
31.00% 26.00% F10157 XL Sago, Ingredion E910-55 55 6 240 28.00%
Polyethylene, Honeywell 2 1 9 30.00% 16.00% ACumist F45 Extrusion
Aids and Binders (as super addition to the inorganics) Fatty acid
na na na 1.40% 1.42% 1.43% 1.43% 1.43% 1.43% 1.43% 1.38% 1.46%
4.08% Binder: F240 3500 50 na 2.10% 6.41% 6.44% 6.44% 6.44% 6.44%
6.44% 2.07% 2.19% 2.04% Binder: TY11A 2100 20 na 4.20% 4.14% 4.38%
1.36% Properties Calculated Na content, ppm 0.064% 0.082% 0.078%
0.072% 0.078% 0.089% 0.073% 0.064% 0.069% 0.063% Calculated K
content, ppm 0.002% 0.003% 0.003% 0.030% 0.002% 0.004% 0.003%
0.002% 0.002% 0.002% Calculated Ca content, ppm 0.033% 0.038%
0.043% 0.036% 0.038% 0.048% 0.038% 0.041% 0.044% 0.038% Total
Calculated Na + K + Ca content, ppm 0.099% 0.122% 0.124% 0.138%
0.118% 0.141% 0.114% 0.107% 0.115% 0.103% Porosity, % 60.6 59.1
61.6 59.7 60.8 60.7 60.2 59.6 62.2 57.8
* * * * *